1. Field of the Invention
The present invention relates to a thiocarbonylthio compound, and more particularly to a radical polymerization process for preparing polymers of vinyl monomers with controlled molecular weight and narrow polydispersity in the presence of the thiocarbonylthio compound.
2. Background of the Invention
Radical polymerization is one of the polymerization processes which are most widely exploited industrially because of the variety of the polymerizable monomers ( greater than 50% of the commercial polymers), of the ease of application and of the synthesis processes employed (emulsion, suspension, bulk, solution). However, in conventional radical polymerization it is difficult to control the size of the polymer chains and the molecular mass distribution. The polymers thus prepared contain chains of very large and very small masses (broad polydispersity), and this results in materials with uncontrolled properties.
Anionic and cationic polymerization techniques, for their part, allow proper control of the process, but the reaction conditions which these polymerization methods require are not always capable of being implemented on an industrial scale. In addition, many monomers cannot be polymerized using these techniques.
Living free radical polymerization is a recently developed technique for the controlled polymerization of vinyl monomers. The significant advantages of this technique permits the preparation of a wide range of different materials which are either difficult to prepare, or not available by other polymerization processes. The architecture, composition of the backbone, inclusion of functionality, and high degree of control over the molecular weight and polydispersity can be achieved by living free radical polymerization.
WO 98/01478 have reported a process of living free radical polymerization which teaches that in the presence of a suitable thiocarbonylthio compound (Zxe2x80x94C(xe2x95x90S)xe2x80x94Sxe2x80x94R, RAFT-agent) to an otherwise conventional free radical polymerization. The so-called RAFT is the abbreviation of reversible addition-fragmentation chain transfer. A polymer with narrow molecular weight distribution can be obtained and the polymer chain length can be freely controlled.
This invention relates to a new thiocarbonylthio system, resulting in a much faster rate for vinyl monomers while still retaining a high degree of control over the molecular weight and polydispersity.
The object of the present invention is to provide a thiocarbonylthio compound.
Another object of the present invention is to provide a thiocarbonylthio compound that can control the radical polymerization of vinyl monomers in a quasi-living manner. Thiocarbonylthio compound of the present invention enhances the rate of polymerization while maintaining low polydispersity.
To achieve the above-mentioned objects, the thiocarbonylthio compound of the present invention is represented by formula (I) 
Wherein
n is an integer of 0 to 3;
R1 is alkyl, haloalkyl, alkenyl, aryl, alkylaryl, haloalkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkoxyaryl, alkyl sulfide, or alkylsilyl;
R2 and R3 are independently H, alkyl, haloalkyl, alkenyl, aryl, alkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkyl sulfide, or alkylsilyl;
R4 and R5 are independently H, alkyl, haloalkyl, alkenyl, aryl, alkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkyl sulfide, or alkylsilyl, or R4 and R5 link together with the carbon atoms to which they are attached to form a ring system; and
Y is O or S.
The living free radical polymerization process of the present invention includes polymerizing at least one kind of vinyl monomer in the presence of the thiocarbonylthio compound represented by formula (I).
The present invention provides a thiocarbonylthio compound represented by formula (I) 
Wherein
n is an integer of 0 to 3;
R1 is alkyl, haloalkyl, alkenyl, aryl, alkylaryl, haloalkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkoxyaryl, alkyl sulfide, or alkylsilyl;
R2 and R3 are independently H, alkyl, haloalkyl, alkenyl, aryl, alkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkyl sulfide, or alkylsilyl;
R4 and R5 are independently H, alkyl, haloalkyl, alkenyl, aryl, alkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkyl sulfide, or alkylsilyl, or R4 and R5 link together with the carbon atoms to which they are attached to form a ring system; and
Y is O or S.
Alkyl referred to in the present invention may contain from 1 to 18, preferably from 1 to 10, carbon atoms. Haloalkyl may have 1 to 18, preferably from 1 to 10, carbon atoms. An example is chloromethyl (xe2x80x94CH2Cl). Aryl may have 6 to 10 carbon atoms, such as phenyl. Alkylaryl or arylalkyl may have 7 to 20, preferably from 7 to 15, carbon atoms. An example of alkylaryl is methylphenyl (xe2x80x94C6H4xe2x80x94CH3), and an example of arylalkyl is phenylmethyl (xe2x80x94CH2xe2x80x94C6H5). Haloalkylaryl may have 7 to 20, preferably from 7 to 15, carbon atoms. An example of haloalkylaryl is trifluoromethylphenyl.
Aminoalkyl referred to in the present invention may contain from 1 to 18, preferably from 1 to 10, carbon atoms. The aminoalkyl may be primary, secondary, or tertiary. Examples include aminomethyl (xe2x80x94CH2xe2x80x94NH2), methylaminomethyl (xe2x80x94CH2xe2x80x94NH(CH3)), and dimethylaminomethyl (xe2x80x94CH2xe2x80x94N(CH3)2).
Alkylamino referred to in the present invention may contain from 1 to 18, preferably from 1 to 10 carbon atoms. The alkylamino may be secondary or tertiary. Examples include methylamino (xe2x80x94NHxe2x80x94CH3) and dimethylamino (xe2x80x94N(CH3)2).
Alkoxy referred to in the present invention may contain from 1 to 18, preferably from 1 to 10, carbon atoms. Examples include methoxy and ethoxy. Alkoxyaryl referred to in the present invention may contain from 7 to 24, preferably from 7 to 16 carbon atoms. An example of alkoxyaryl is methoxyphenyl.
Alkyl sulfide may contain from 1 to 18, preferably from 1 to 10, carbon atoms. An example is methyl sulfide (xe2x80x94Sxe2x80x94CH3). Alkylsilyl may contain from 1 to 20, preferably from 1 to 10, carbon atoms. Examples include trimethylsilyl (xe2x80x94Si(CH3)3), dimethylsilyl (xe2x80x94SiH(CH3)2), and dimethylethylsilyl (xe2x80x94Si(CH3)2(C2H5)).
Preferably, R1 is alkyl, aryl, alkylaryl, alkoxyaryl, or haloalkylaryl, and R2 and R3 are independently H, alkyl, haloalkyl, alkenyl, aryl, alkylaryl, or arylalkyl.
R4 and R5 can be independently H, alkyl, haloalkyl, alkenyl, aryl, alkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkyl sulfide, or alkylsilyl, and preferably H, alkyl, haloalkyl, alkenyl, aryl, alkylaryl, or arylalkyl. Or, alternatively, R4 and R5 can link together with the carbon atoms to which they are attached to form a ring system having from 4 to 20 carbon atoms. The ring system can be a saturated ring or an unsaturated ring such as an aromatic ring.
According to a preferred embodiment of the present invention, the thiocarbonylthio compound of the present invention can be represented by formula (II), 
Wherein
n is an integer of 0 to 3;
R1 is alkyl, haloalkyl, alkenyl, aryl, alkylaryl, haloalkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkoxyaryl, alkyl sulfide, or alkylsilyl;
R2 and R3 are independently H, alkyl, haloalkyl, alkenyl, aryl, alkylaryl, arylalkyl, aminoalkyl, alkylamino, alkoxy, alkyl sulfide, or alkylsilyl;
Y is O or S.
Compared to the thiocarbonylthio compounds reported in WO 98/01478, the above thiocarbonylthio compound is easy to synthesize and obtained as crystals in high yield. No further purification method like column chromatography is required.
In the presence of the thiocarbonylthio compound represented by formula (I) of the present invention, the polymerization has living characteristics and provides polymers of controlled molecular weight and low polydispersity.
The monomer that is polymerized can be one vinyl monomer alone, or in combination with one or more polymerizable vinyl comonomers.
Specific monomers include the followings: acrylic acid and its salts, acrylates, methacrylic acid and its salts, methacrylates, acrylonitriles, styrenes, acrylamides, butadiene, isoprene or mixtures thereof. Representative examples include methyl acrylate, ethyl acrylate, propyl acrylate (all isomers), butyl acrylate (all isomers), 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, isobornyl acrylate, acrylic acid, benzyl acrylate, phenyl acrylate, acrylonitrile, styrene, N,N-dimethylaminoethyl methacrylate, methacrylamides, acrylamides, N-isopropyl acrylamide, methyl methacrylate etc.
In the presence of the thiocarbonylthio compound represented by formula (I), together with a free radical initiator, the molecular weight of the polymer obtained can be predetermined. The polydispersity of the polymer obtained is usually in a range from 1.05 to 2, and preferably decreased to a range from 1.05 to 1.5, and more preferably decreased to a range from 1.05 to 1.3.
The compound capable of generating free radicals suitable for use in the present invention is not limited and can be any suitable for use in the conventional free radical polymerization, such as AIBN, diacyl peroxides, and di-tert-butyl peroxide.
Using the present invention, the polymer obtained can be a homopolymer or a copolymer. Various copolymers with a well-defined structure can be obtained, including (1) block copolymers (two or more blocks) with narrow polydispersity, (2) graft copolymers with narrow polydispersity, (3) gradient copolymers, (4) star copolymers, and (5) hyperbranched copolymers. Various polymers with a terminal functional group can also be prepared. The emergence of various novel polymers can provide new materials with new physical properties to be applied in industry. This will not only enhance the performance of the existing products, but also speed up the development of new products. The polymeric materials developed in the present invention can be applied in many fields, including dispersants such as pigment dispersants in ink, photoresists, surfactants, surface treating agents, adhesives, rheology controllers, coatings, and thermoplastic elastomers.